FreeOTP is an open-source two-factor authentication (2FA) application for mobile devices. It is designed to work with websites, cloud services, and other applications that support the one-time passcode (OTP) based authentication method. FreeOTP allows users to generate and store their own OTPs for use in authenticating with various services. It also provides users with a secure backup system for their OTPs, allowing them to store multiple OTPs in one place. FreeOTP also includes a password generator to help users create strong passwords for their accounts. FreeOTP is available for iOS and Android devices, as well as for a web browser.
FreeOTP does 2FA, Authy does a ton more / else. Also, it doesn't have a Windows Phone app.